The present invention relates to a method and apparatus for testing a composite type magnetic head which has a read head portion with a magnetoresistive effect (MR) element for reproducing data from a magnetic medium such as a magnetic disk, and a write head portion with an inductive element for recording data into the magnetic medium.
The composite type magnetic heads described above have been broadly utilized as thin-film magnetic heads for reading data from and/or writing data into the magnetic medium such as the magnetic disk. Recently, a magnetic head with a giant magnetoresistive effect (GMR) element such as a spin-valve MR element or with a tunnel magnetoresistive effect (TMR) element has been developed to increase magnetic recording density, instead of a usual magnetic head with an anisotropic magnetoresistive effect (AMR) element.
At each test after manufacturing such a magnetic head, it is necessary to confirm that the finished magnetic head with a MR element is a good article and may not produce any inherent noise such as Barkhausen noise. Japanese Patent Unexamined Publication No.6 (1994)-150264 of the same assignee as that of the present application discloses a MR head testing method. In this testing method, an external alternating magnetic field is applied, in a direction perpendicular to an Air Bearing Surface (ABS), to a plurality of MR heads which are aligned on a head block and are not yet individually separated, and electromagnetic transfer characteristics of each of the MR heads under the varying external magnetic field is measured. By means of this conventional testing method, whether Barkhausen noise is produced or not can be easily checked.
U.S. Pat. No. 5,721,488 of the same assignee as that of the present application discloses an improved MR head testing method. In this testing method, alternating leakage magnetic field with a high frequency excited by a write current flowing through an inductive element is applied to the MR element in addition to external alternating magnetic field which is applied to the MR element in a direction perpendicular to the ABS of the head block, and electromagnetic conversion characteristics of each of the MR heads under the varying external and leakage magnetic fields is measured. By means of this testing method disclosed in the U.S. patent, possible Barkhausen noise can be detected with a high probability.
These known testing methods using the electromagnetic conversion characteristics measuring device can be used for detecting whether Barkhausen noise is produced or not but cannot be applied for detecting instability of output of the MR element, which is different from abnormal output of the MR element due to Barkhausen noise. In fact, when outputs of the MR element of the composite type magnetic head are repeatedly measured many times by means of the electromagnetic conversion characteristics measuring device, the output wave shapes of the MR element may sometimes vary due to some reason and thus the same output level cannot always be obtained, resulting poor reproducibility.
Therefore, according to the conventional testing method, it is impossible to detect instability of output of the MR element except when the test is repeated many times to increase the probability of the detection. However, repeating the test numerous times will lower the manufacturing efficiency of the head.
Particularly, the composite type magnetic head with the GMR element or the TMR element may very easily trigger the output instability because such magnetic head has high sensitivity and a complicated structure and therefore is susceptible to its environment.
In order to solve the above-mentioned problems with respect to instability of the MR output, the inventors of this application have already proposed a method for testing a composite type magnetic head having a MR element and an inductive element, by applying a first current with one polarity to the inductive element, by measuring output characteristics of the MR element, by applying a second current with the other polarity to the inductive element, and by measuring the output characteristics of the MR element (U.S. Ser. No. 09/196,442, now pending).
It should be noted that it is very important for a magnetic head with a MR element to measure instability of an output of the MR element around its bias point or a point at which the magnetic field in the electromagnetic conversion characteristics is zero, otherwise instability would be caused by the shield layer of the MR element. This is because the bias point is located at the center of the output signal from the MR element and thus it is impossible to obtain a correct output signal from the MR element if the bias point is offset.
The conventional testing method with application of external alternating magnetic field to the MR element can measure a deviation of such bias point. However, in order to measure the bias point deviation according to the conventional testing method, it is necessary to find a point of zero magnetic field by using a magnetic field generation device. This causes a complicated structure of the testing apparatus and requires an extreme amount of time.
It is therefore an object of the present invention to provide a method and apparatus for testing a composite type magnetic head, whereby an easy and reliable test can be attained with respect to the instability of the output of a MR element around its bias point.
According to the present invention, a method for testing a composite type magnetic head having a MR element and an inductive element includes a current application step of applying a current to the inductive element, with applying no external magnetic field to the magnetic head, and a measurement step of measuring output characteristics of the MR element after the current application step is finished.
Output characteristics of the MR element is not merely measured but is measured under a condition wherein possible instability of the output of the MR element around its bias point will be intentionally induced by forcefully applying to the inductive element a current which will change an initial magnetization state of a shield layer for the MR element. According to the present invention, particularly, since the output voltage characteristics of the MR element is measured after the current is applied to the inductive element without an external magnetic field, being applied, the wave shape of the output voltage from the MR element directly indicates the wave shape around the bias point of the MR element. Thus, the performance evaluation of the magnetic head over its actual operation region can be executed very easily. Furthermore, since any influence due to the applied external magnetic field such as temporal suppression of occurred output instability due to the applied external magnetic field is not exerted, the evaluation of the head itself can be performed correctly and certainly.
It is preferred that the application step and the measurement step are repeated at least twice.
It is preferred that the current application step includes an application step of applying a rectangular wave shape current with a predetermined polarity such as positive or negative polarity to the inductive element.
It is also preferred that the current application step includes an application step of applying a rectangular wave shape current with an alternating polarity to the inductive element.
It is also preferred that the current application step includes an application step of applying a high frequency rectangular wave shape current to the inductive element.
According to the present invention, also, an apparatus for testing a composite type magnetic head having a MR element and an inductive element, includes a first current application unit for applying a current to the inductive element, with applying no external magnetic field to the magnetic head, a second current application unit for applying a sense current to the MR element, and a measurement unit for measuring output characteristics of the MR element by receiving output voltage from the MR element after the application of the current to the inductive element from the first current application unit is finished while the sense current from the second current application unit is flowing.
Furthermore, according to the present invention, an apparatus for testing a composite type magnetic head having a MR element with terminals and an inductive element with terminals, includes a probe unit for electrically contacting to the terminals of the MR element and to the terminals of the inductive element, a first current application unit for applying a current to the inductive element through the probe unit, with applying no external magnetic field to the magnetic head, a second current application unit for applying a sense current to the MR element through the probe unit, and a measurement unit for measuring output characteristics of the MR element by receiving output voltage from the MR element through the probe unit after the application of the current to the inductive element from the first current application unit is finished while the sense current from the second current application unit is flowing.
The output characteristics of the MR element is measured after the application of the current to the inductive element from the first cent application unit with applying no external magnetic field is finished. Thus, the wave shape of the output voltage from the MR element directly indicates wave shape around the bias point of the MR element. As a result, performance evaluation of the magnetic head over its actual operation region can be executed very easily. Furthermore, since any influence due to the applied external magnetic field such as temporal suppression of occurred output instability due to the applied external magnetic field is not exerted, evaluation of the head itself can be performed correctly and certainly. In addition, since it is not necessary to apply external magnetic field, apparatus configuration becomes simpler.
It is preferred that the application unit and the measurement unit repeat the application of the current to inductive element and the measurement of output characteristics of the MR element after the application of the current is finished, at least twice.
It is preferred that the first current application unit includes an application unit for applying a rectangular wave shape current with a predetermined polarity such as positive or negative polarity to the inductive element.
It is also preferred that the first current application unit includes an application unit for applying a rectangular wave shape current with an alternating polarity to the inductive element.
It is also preferred that the first current application unit includes an application unit for applying a high frequency rectangular wave shape current to the inductive element.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.